The invention relates to a method for electrical testing of a unit under test, which is connected via a contact-making apparatus to an electrical test device. The contact-making apparatus has a plurality of electrical contacts on at least one holding element for making contact with mating contacts on the unit under test. The contacts and the mating contacts are positioned with respect to one another with the assistance of optical detection processes of the contact-making apparatus and the unit under test.
In order to carry out an electrical function test on an electrical unit under test, for example a wafer, this unit is connected to an electrical test device by means of a contact-making apparatus. The contact-making apparatus has electrical contacts on at least one holding element, in order to make contact with mating contacts on the unit under test. The contacts and mating contacts are aligned relative to one another with the aid of an optical device. Contact is then made, that is, the mating contacts on the unit under test make touching contact with the contacts on the contact-making apparatus. The electrical test device is thus connected to the unit under test, so that continuity measurements, isolation measurements etc. can be carried out. The optical device, which is preferably in the form of a camera, is not used to detect all of the contacts on the contact-making apparatus, in order to speed up the test process. The detection process is carried out in particular only at significant points, for example by detection of corner contacts. This results in a risk of an incorrect position being calculated for making contact when, for example, a plurality of identical or similar contact patterns occur in the contact-making apparatus.
Furthermore, a contact-making apparatus is known having electrical contacts that are pressed against mating contacts on the unit under test in order to test such a unit. The contact-making apparatus is connected to an electrical test device, so that the unit under test can be electrically tested via the current paths that have been created. For example, wafers for the manufacture of semiconductor chips can be tested in this way. In order to allow a good contact to be made between the unit under test contacts which form the mating contacts and the contacts on the contact-making device, it is known for the position of the contacts of the contact-making apparatus and the position of the mating contacts of the unit under test to be detected by means of a camera, or a camera system, and to be made to coincide, that is, be aligned by appropriate movement of the contact-making apparatus and/or of the unit under test. In order to speed this process, the camera does not detect all of the contacts of the contact-making apparatus, but only detects significant points, such as corner contacts, that is, contacts which are located at the corner points of the contact arrangement. In the case of multiple probing, that is a test in which, for example, a plurality of IC chips on a wafer are tested at the same time, there is a risk that an incorrect position will be calculated for making contact, since there are a plurality of identical or similar contact patterns in the contact-making apparatus and/or the unit under test. There is also a risk the alignment process may take a very long time, or may even have to be carried out manually.